Anopheline larval habitats seasonality and species distribution: a prerequisite for effective targeted larval habitats control programmes

Abstract

Background: Larval control is of paramount importance in the reduction of malaria vector abundance and subsequent disease transmission reduction. Understanding larval habitat succession and its ecology in different land use managements and cropping systems can give an insight for effective larval source management practices. This study investigated larval habitat succession and ecological parameters which influence larval abundance in malaria epidemic prone areas of western Kenya.

Methods and findings: A total of 51 aquatic habitats positive for anopheline larvae were surveyed and visited once a week for a period of 85 weeks in succession. Habitats were selected and identified. Mosquito larval species, physico-chemical parameters, habitat size, grass cover, crop cycle and distance to nearest house were recorded. Polymerase chain reaction revealed that An. gambiae s.l was the most dominant vector species comprised of An.gambiae s.s (77.60%) and An.arabiensis (18.34%), the remaining 4.06% had no amplification by polymerase chain reaction. Physico-chemical parameters and habitat size significantly influenced abundance of An. gambiae s.s (P = 0.024) and An. arabiensis (P = 0.002) larvae. Further, larval species abundance was influenced by crop cycle (P≤0.001), grass cover (P≤0.001), while distance to nearest houses significantly influenced the abundance of mosquito species larvae (r = 0.920;P≤0.001). The number of predator species influenced mosquito larval abundance in different habitat types. Crop weeding significantly influenced with the abundance of An.gambiae s.l (P≤0.001) when preceded with fertilizer application. Significantly higher anopheline larval abundance was recorded in habitats in pasture compared to farmland (P = 0.002). When habitat stability and habitat types were considered, hoof print were the most productive followed by disused goldmines.

Conclusion: These findings suggest that implementation of effective larval control programme should be targeted with larval habitats succession information when larval habitats are fewer and manageable. Crop cycles and distance from habitats to household should be considered as effective information in planning larval control.

Figure 1. A map showing the study sites and habitat types used during the study period in western Kenya Highlands.

Figure 2. Types of habitats used for larvae abundance in different land use types.

Figure 3. Mosquitoes larvae diversity index by Simpson model in 85 weeks of survey.

Figure 4. Anopheles gambiae s.s and An. arabiensis larvae abundance and dynamics among identified specimen throughout 85 weeks of field surveys.

Figure 5. Mosquitoes larvae per dip in different (5A) crop cycle, (5B) seasonality, (5C) habitat types and (5D) land use types during 85 weeks of larvae abundance survey.

Figure 6. Mosquito larvae per dip in different grass cover (canopy) during 85 weeks of larvae abundance survey.